Burner control system



March 25, 1969 J. A. WRIGHT BURNER CONTROL SYSTEM Filed 061;. 1a, 1967 NVEN 7'02 JAMES A WEIGHT J) 444 ZM United States Patent US. Cl. 431-66 4Claims ABSTRACT OF THE DISCLOSURE A gas burner control system having anelectrically energized glow coil igniter positioned so as to be impinged by burner flame and a photoconductive sensor which is insensitiveto gas flame but is responsive to radiant energy of the glow coil whenit is at ignition temperature to effect the flow of gas to the burnerand to reduce the electrical energization level of the coil, and inwhich a sumcient glow coil temperature is maintained at the reducedelectrical energization level due to its being positioned in the burnerflame to effect a continued response of the sensor which will maintainthe flow of gas to the burner.

An object of the invention is to provide a simple and reliable safetycontrol system for gas burners employing a metallic, electricalresistance, glow coil igniter which is electrically energized toignition temperature only until ignition of the gas occurs and isthereafter during burner operation energized to a lesser degree in orderto extend the life of the coil.

A further object is to provide an arrangement in which the electriccurrent flow through a fuel control relay electrically connected inseries with a photoconductive cell varies with the temperature of anelectrically energized igniter glow coil which activates the cell, inwhich the igniter coil is initially electrically energized to gasignition temperature to ignite the burner and to effect suflicientconduction through the photoconductive cell and relay to cause the relayto close to a fuel supplying position, and in which the temperature ofthe igniter coil is reducedupon closure of the relay by reducing itselectrical energization level to that which will activate suflicientconduction through the photoconductive cell and relay to hold the relayclosed but not sufficient to move the relay closed from an openposition.

A further object is to provide an arrangement as in the foregoingparagraph in which the igniter coil is positioned in the burner flame,in which the electrical energization level of the igniter coil isreduced upon closure of the relay to a level below that which will heatthe coil sufliciently to hold the relay closed, and in which heating ofthe coil by the burner flame raises its temperature to that which willactivate suflicient conduction through the photoconductive cell andrelay to hold the relay closed whereby a flame failure will result inopening of the relay.

A further object is to provide an arrangement as set forth in the twopreceding paragraphs in which the igniter glow coil is constructed of amaterial such as platinum which catalyzes combustion of the gas, and inwhich catalytic action as well as heating of the igniter coil by theburner flame supplements the resistance heating of the glow coil toprovide a temperature thereof which will activate the photocell toconduction which is suflicient to hold the relay closed but isinsufficient to close it.

Other objects and advantages of the invention will appear from thefollowing description when read in connection with the accompanyingdrawing.

FIG. 1 of the drawing is a schematic diagram of a gas burner controlsystem constructed in accordance with the present invention;

FIG. 2 is a side elevational view of the control relay and its switchingconstruction.

Referring to the drawing, a gas burner is indicated at 10 to which gasis supplied from a suitable source through conduit 12. A normally closedsolenoid valve 14 having a winding 15 is interposed in conduit 12 andcontrols the flow of gas to the burner 10. The burner 10 is ignited by aplatinum or platinum alloy glow coil igniter 16. The glow coil igniteris positioned in the path of gas issuing from the burner 10 and isimpinged by flame when the burner is ignited. Low voltage current issupplied to glow coil 16 by a voltage step-down transformer 20 having asecondary winding 22 and a primary winding 24.

Other primary elements of the system are: a photoconductive sensingdevice 26, a relay generally indicated at 28 having a winding 30, aswitch blade 32 and a contact 36, a current limiting resistor 37, aheating resistor 38, a bimetal switch 39 having a contact 4.1, a fuse40, a thermostat 42, a double-throw manual switch 44, and a pair ofterminals 46 and 48 for connection to a commercial power source.

The photoconductive sensing device 26 is a cadmium sulphite, solid statedevice directed so as to be activated by radiant energy from glow coil16. The device 26 has extremely high resistance to the flow ofelectrical current when inactivated by [radiant energy and becomessufliciently conductive for the purposes to be described when the glowcoil igniter is heated to predetermined temperatures. Inasmuch as thefrequency response curve of a cadmium sulphite sensing cell peaks in theinfrared band and falls to zero in the yellow band, activation of thecell by radiant energy from an efficiently operating blue flame gasburner is negligible.

The relay 28, shown in FIG. 2, is biased in the deenergized openposition, as shown in FIG; 2, by a spring 35. In this open positionswitch blade 32 is open with respect to contact 36. When winding 30 issufficiently energized the blade 32 moves to a closed position withcontact 36, as shown in dotted line. The relay 28 being biased open withits clapper 32 spaced from its core 33, it requires a higher value ofenergization of winding 30 (more current flow) to effect its closing tothe dotted position than is required to hold it in this closed positionwith the clapper 32 against core 33. The relay may, therefore, be heldin the closed dotted line position at a lower energization value of coil30 than is required to move it to a closed position.

This ditferential in the required energization value of winding 30between closing and holding closed the relay is further increased by theprovision of a permanent magnet 53 which cooperates with an armature 55carried by switch blade 32 to provide a slight additional force holdingthe relay closed. The additional holding force provided by permanentmagnet 53 requires a still further reduction in the current flow throughrelay winding 30 to permit biasing spring 35 to move blade 32 to itsopen position.

The relay winding 30 is connected across the power supply terminals 46and 48 in series with the double-throw manual switch 44, the thermostat42, the photoconductive cell 26, and the fuse 40, by leads 52, 54, 56,58, 60, 62, and 64.

The primary winding 24 of ignition transformer 20 is connected acrossthe power supply terminals 46 and 48 in series with switch 44,thermostat 42, and normally closed bimetal switch 39, by leads 52, 54,56, 65, 67, 69, 72, and 64. The ignition transformer primary winding 24is also connected across the bimetal switch 39 through a resistor 37 bythe leads 75 and 76.

The resistor 38, in heat transfer relationship with bimetal switch 39,is connected across the power supply terminals in series with the manualswitch 44, thermostat 42, the switch blade 32 and contact 36, by leads52, 54, 56, 66, 71, 73, 74, and 64. When the resistor 38 is energized,it causes the bimetal switch 39 to warp open with respect to its contact41 in a relatively short time, as in the order of two or three seconds.

The solenoid valve winding is connected across the power supplyterminals in series with manual switch 44, thermostat 42, relay switchblade 32 and contact 36 by leads 52, 54, 56, 66, 71, 68, 70, and 64.

The photoconductive cell 26 is also connected across the power supplyterminals 4648 in series with fuse 40 through the hot side (dotted line)of thermostat 42 and the open side (solid line) position of double-throwmanual switch 44 by leads 52, 54 or 57, 78, 58, 69, and 64.

OPERATION When it is desired to operate the burner, the doublethrowmanual switch 44 is moved from its open solid line position shown to itsclosed dotted line position. The closing of switch 44 completes thecircuit connecting ignition transformer primary winding 24 across thepower supply terminals 46-48 through the thermostat 42 (in its coldposition shown) and through bimetal switch 39. The transformer primarywinding 24 is now connected directly across the power supply and theglow coil 16 being fully energized to a high level quickly heats toignition temperature. The photoconductive cell 26 is activated to a highlevel of conductivity by the glow coil and effects the pull in of relay28 causing the switch blade 32 to close with contact 36.

When relay switch blade 32 closes with contact 36 the described circuitthrough winding 15 of the normally closed solenoid valve 14 iscompleted, causing the valve to open and gas to flow from burner 10 tobe ignited by glow coil 16. The closing of relay blade and contact 32-36 also connects the heating resistor 38 across the power supply, andafter a short period of two or three seconds, the resistor 38 causesbimetal blade 39 to warp away from its contact 41, thereby limiting theflow of current through transformer primary 24 to that permitted bycurrent limiting resistor 37. This reduction in current flow throughprimary 24 by resistor 37 reduces the temperature of glow coil 16 tothat which, in the absence of a burner flame, is insufficient toactivate photoconductive cell 26 to a conductivity which will hold therelay in its closed dotted line position.

In normal operation burner flame occurs within one or two seconds afterthe closing of relay 28 and the energization of the solenoid valve, sothat flame is now impinging the glow coil. The burner flame, togetherwith catalytic action of the platium coil, raises the temperature of theglow coil 16 sufficiently above that to which it is energized throughresistor 37 to effect a conduction through the sensing device 26 andrelay winding 30 which will hold the relay 28 open. The temperaturewhich the coil will attain when its energization is limited by resistor37 will not, however, even with the supplementary heating or shroudingof the flame and catalysis, approach that necessary to effect aconduction through cell 26 which will pull in relay 28. It will be notedthat after the relay is closed in normal operation, and until resistor38 heats bimetal switch 39 sufficiently to open it, the glow coil 16will be energized to ignition temperature. When the thermostat issatisfied during normal burner operation and moves to its hot dottedline position, the igniter will be completely disconnected.

The fuse 40 is calibrated to burn out at a slightly higher current flowthan that required to effect the pull in of relay 28 so that if thephotocell 26 breaks down and becomes conductive at any time when manualswitch 44 is open or the thermostat is in its hot position, the relay 28will not be pulled in. The photocell being connected across the powersource terminals in series with the fuse 40 through the manual switch 44when open (solid line position), and through the manual switch 44 andthermostat 42 when the manual switch is closed (dotted line position)and the thermostat 42 is in its hot (dotted line) position, a failure ofthe photocell during inoperation of the burner will effect a burn out offuse 40 and prevent subsequent pull in of relay 28 when switch 44 isclosed and thermostat 42 moves to a cold demand position.

If the photoconductive cell becomes faulty during burner operation andbecomes abnormally conductive, it may not burn out the fuse due to theimpedance of relay coil 30, but as soon as the thermostat is satisfiedand moves to its dotted line position, the photocell and fuse will bedirectly connected across the power source and the fuse will be causedto burn out, thereby preventing a reopening of valve 14 upon subsequentclosure of the thermostat.

I claim:

1. In a burner control system, a burner, a source of electrical power, anormally closed fuel valve, an electric glow coil igniter, circuit meansconnecting said igniter across said power source effecting the heatingthereof to ignition temperature, a relay including a winding, said relayhaving a biased open position and an energized closed position to whichit moves when its winding is fully energized, a photoconductive cell,circuit means connecting said photoconductive cell and said relaywinding in series relationship across said power source, saidphotoconductive cell being responsive to the radiant energy of said glowcoil and becoming sufficiently conductive when said glow coil is atignition temperature to permit full energization of said seriesconnected relay winding and effect the closing of said relay, meansrendered operative when said relay closes to effect the opening of saidnormally closed fuel valve, and means rendered operative when said relaycloses to effect a reduction in current flow through said glow coil, andtherefore its temperature, to that which will effect a conductivity ofsaid photocond-uctive cell sufficient to hold said relay closed but lessthan that required to close it.

2. A burner control system as set forth in claim 1 in which said glowcoil is constructed of a material which catalyses the combustion of thefuel, in which said glow coil is positioned so as to be in the path ofthe fuel issuing from said burner and impinged by burner flame, and inwhich the heating of the glow coil by the reduced electrical currentflow therethrough, and the heating by catalysis and burner flame,maintains a temperature thereof which activates said photoconductivecell to conductivity suflicient to hold said relay closed butinsufficient to close If.

3. A burner control system as set forth in claim 1 in which said relayincludes detent means rendered operative upon closure of said relay torequire a greater reduction in current flow through said relay windingto permit its return from its closed position to its biased openposition.

4. A burner control system as set forth in claim 1 in which said circuitmeans connecting said glow coil across said power source includes anormally closed heat opened bimetal switch, and a current droppingresistor connected 5 across said bimetal switch, and in which said meansrendered operative upon closure of said relay to effect a reduction incurrent flow through said glow coil comprises a resistance heater forheating said bimetal switch and circuit connections completed uponclosure of said relay 1O connecting said resistance heater across saidpower source.

6 References Cited UNITED STATES PATENTS 3/1963 Wright et a1. 431-6610/1964 Matthews 431-66 X FREDERICK L. MA'ITESON, JR., Primary Examiner.ROBERT A. DUA, Assistant Examiner.

US. Cl. X.R. 431-70

